Night of poetry held in Middle England (3)
I believe the answer is:
een
'night of poetry' is the definition.
(poetic term for evening or night)
'held in middle england' is the wordplay.
'held in' indicates a hidden word.
'EEN' can be found hidden inside 'middle england'.
(Other definitions for een that I've seen before include "Literary form of even" , "Poetic form of even" , "Even, poetically" , "Even to the poet" .)